When schistosome cercariae leave fresh water to penetrate the skin of a human host, both biochemical and morphological changes accompany the transformation into schistosomule. In either cercariae or early schistosomula we expect that within the pool of messenger RNAs (mRNA), there is a class of mRNA encoding for the surface antigens that allow susceptibility of the schistosomule to the concomitant immune response of an infected host. Because these surface antigens are critical in the development of a vaccine their identification and production is timely and important. We will examine the genetic control and expression of these schistosome surface antigens. Initially, we will use antibodies (IgG) found in serum from chronically infected vertebrate hosts to identify them. (In early experiments we have already had success in identifying iodinated schistosomular surface antigens.) Later we will use monoclonal antibodies that will be directed against the same and other surface determinants. Poly-A containing mRNA will be isolated from schistosomula, translated in vitro and the protein products screened by immunoprecipitation. The mRNA will be separated according to size allowing us to enrich for mRNA's of interest. This mRNA will then be used to produce cDNA using reverse transcriptase. This cDNA will be cloned into plasmids and the cDNA clones selected by hybrid arrested translation to identify clones of interest. Once we obtain the desired cDNA's we will use them as probes to study the genetic expression of antigens of interest and to engineer expression of the antigens in Escherichia coli. We will also create a genomic library of schistosome DNA in bacteriophage lambda. This will give us an additional source of DNA complementary to mRNA's of interest and allow us to begin to explore the regulation of expression of mRNA encoding surface antigens.